1. Field of the Invention.
The present invention relates to a method and apparatus for direct or indirect application of a liquid or pasty medium onto a traveling material web, notably of paper or cardboard.
2. Description of the Related Art.
Known from German Patent Document No. 44 32 177 A1 is an applicator system for direct or indirect application of a liquid or pasty medium onto a traveling material web. The described applicator system is one with an open-jet nozzle formed by two oblong lip elements. The metering slot of the open-jet nozzle, that is, the clearance between the two lip elements, allows zonewise adjustment across the length of the lip elements, i.e., across the width of the material web to be coated. Hence, the amount of application of the liquid or pasty medium can be metered differently zonewise on the open-jet nozzle.
To that end, a plurality of adjustment apparatuses are provided, which are distributed across the length of the lip elements and act at least on one of the two lip elements of the open-jet nozzle. Also provided is an automatic control loop which readjusts the adjustment apparatuses on the basis of measured values of the cross profile of the applied liquid or pasty medium. The open-jet nozzle applicator system may also be followed by a precision metering apparatus which, by means of a doctor element, for example a doctor blade, removes liquid or pasty medium applied at surplus to the desired final cross profile.
The unpublished patent application No. 196 05 183.5 describes a method for control of the cross profile of the applied liquid or pasty medium existing across the width of the material web, the method relating to an applicator system such as explained above. Two control loops are provided, one of which effects a first correction of the cross profile directly on the open-jet nozzle. The second control loop effects on the precision metering apparatus a second and final correction of the cross profile of applied liquid or pasty medium. The two corrections are meant to supplement one another in their effect to obtain a desired overall correction of the cross profile. While a desired cross profile of relatively high accuracy is obtained with the proposed method, the control-related expense required, in addition to the mechanical expense, is considerable.